Liquid crystalline medium

ABSTRACT

wherein the parameters have the meaning given in claim 1 and to liquid crystal displays comprising these media, especially to active matrix displays and in particular to TN and IPS mode displays.

The present invention relates to liquid crystalline media and to liquidcrystal displays comprising these media, especially to displaysaddressed by an active matrix and in particular to displays of theTwisted Nematic or the In Plane Switching (IPS) type.

Liquid Crystal Displays (LCDs) are widely used to display information.LCDs are used for direct view displays, as well as for projection typedisplays. Electro-optical modes employed are e.g. the twisted nematic(TN)-, the super twisted nematic (STN)-, the optically compensated bend(OCB)- and the electrically controlled birefringence (ECB)-mode withtheir various modifications, as well as others. All these modes use anelectrical field, which is substantially perpendicular to thesubstrates, respectively to the liquid crystal layer. Besides thesemodes there are also electro-optical modes employing an electrical fieldsubstantially parallel to the substrates, respectively the liquidcrystal layer, like e.g. the In-Plane Switching mode (as disclosed e.g.in DE 40 00 451 and EP 0 588 568). Especially this electro-optical modeis used for LCDs for modern desktop monitors and TV applications. Theliquid crystals according to the present invention are preferably usedin this type of displays.

For these displays new liquid crystalline media with improved propertiesare required. Especially the response times have to be improved for manytypes of applications. Thus liquid crystalline media with lowerviscosities (η), especially with lower rotational viscosities (γ₁) arerequired. The rotational viscosity should be 80 MPa·s or less,preferably 70 MPa·s or less and especially 60 MPa·s or less. Besidesthis parameter, the media have to exhibit a suitably wide range of thenematic phase, an appropriate birefringence (Δn) and dielectricanisotropy (Δε) should be high enough to allow a reasonably lowoperation voltage. Preferably Δε should be higher than 3 and verypreferably higher than 4, preferably, however, not higher than 15 and inparticular not higher than 12, as this would be detrimental for an atleast reasonably high specific resistivity.

The displays according to the present invention are preferably addressedby an active matrix (active matrix LCDs, short AMDs), preferably by amatrix of thin film transistors (TFTs). However, the inventive liquidcrystals can also beneficially be used in displays with other knownaddressing means.

There are various different display modes using composite systems ofliquid crystal materials of low molecular weight together with polymericmaterials. These are e.g. polymer dispersed liquid crystal (PDLC)-,nematic curvi-linearly aligned phase (NCAP)- and polymer network(PN)-systems, as disclosed for example in WO 91/05 029 or axiallysymmetric microdomain (ASM) systems and others. In contrast to these,the modes especially preferred according to the instant invention areusing the liquid crystal medium as such, oriented on surfaces. Thesesurfaces typically are pre-treated to achieve uniform alignment of theliquid crystal material The display modes according to the instantinvention preferably use an electrical field substantially parallel tothe composite layer.

Liquid crystal compositions suitable for LCDs and especially for IPSdisplays are known e.g. from JP 07-181 439 (A), EP 0 667 555, EP 0 673986, DE 195 09 410, DE 195 28 106, DE 195 28 107, WO 96/23 851 and WO96/28 521. These compositions, however, do have significant drawbacks.Most of them, amongst other deficiencies, lead to unfavourably longresponse times, have too low values of the resistivity and/or requireoperation voltages, which are too high.

Thus, there is a significant need for liquid crystalline media withsuitable properties for practical applications such as a wide nematicphase range, appropriate optical anisotropy An, according to the displaymode used, a high Ac and especially low viscosities.

Surprisingly, it has now been found that liquid crystalline media with asuitably high Ac, a suitable phase range, and An can be realized whichdo not exhibit the drawbacks of the materials of the prior art or atleast do exhibit them to a significantly lesser degree by using liquidcrystalline media comprising one or more compounds of formula I below.

Hence, the present invention relates to a liquid crystal mediumcomprising

-   -   one or more compounds of formula I

wherein

-   R¹ denotes alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy    with 1 to 7 C-atoms, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated    alkenyl with 2 to 7 C-atoms, preferably alkyl or alkenyl,-   L¹ denotes H or F    -   optionally, one or more compounds selected from the group of        compounds of formulae II and III

wherein

-   R² and R³ independently of each other, denote alkyl, alkoxy,    fluorinated alkyl or fluorinated alkoxy with 1 to 7 C-atoms,    alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl with 2 to 7    C-atoms, preferably alkyl or alkenyl,

are independently of each other

preferably

-   L²¹, L²²,-   L³¹ and L³² independently of each other, denote H or F, preferably F-   X² and X³ independently of each other, denote halogen, halogenated    alkyl or alkoxy with 1 to 3 C-atoms or halogenated alkenyl or    alkenyloxy with 2 or 3 C-atoms, preferably F, Cl, —OCF₃ or —CF₃,    most preferably F, Cl or —OCF₃,-   Z³ denotes —CH₂CH₂—, —CF₂CF₂—, —COO—, trans-—CH═CH—, trans-CF═CF—,    —CH₂O— or a single bond, preferably —CH₂CH₂—, —COO—, trans-—CH═CH—    or a single bond and most preferably —COO—, trans-—CH═CH— or a    single bond, and-   I, m, n and o are, independently of each other, 0 or 1 and from    which compounds of formula I are excluded, and    -   optionally one or more compounds of formula IV

wherein

-   R⁴¹ and R⁴² independently of each other have the meaning given for    R² under formula II above, preferably R⁴¹ is alkyl and R⁴² is alkyl    or alkoxy or R⁴¹ is alkenyl and R⁴² is alkyl,

independently of each other, and in case

is present twice, also these, independently of each other, are

preferably at least one of

-   Z⁴¹, Z⁴² independently of each other, and in case Z⁴¹ is present    twice, also these independently of each other, denote —CH₂CH₂—,    —COO—, trans-—CH═CH—, trans-—CF═CF—, —CH₂O—, —CF₂O—, —C═C— or a    single bond, preferably at least one of them is a single bond, and-   p is 0, 1 or 2, preferably 0 or 1.

The compounds of formula II are preferably selected from the group ofcompounds of formulae II-1 to II-3

wherein the parameters have the respective meanings given under formulaII above and in formula II-1 the parameters L²³ and L²⁴ denote,independently of each other and of the other parameters, H or F and informula II-2 preferably

denote independently of each other

In formulae II-1 to II-3, L²¹ and L²² or L²³ and L²⁴ are preferably bothF.

In another preferred embodiment in formulae II-1 and II-2, all of L²¹,L²², L²³ and L²⁴ denote F.

The compounds of formula II-1 are selected from the group of compoundsof formulae II-1a to II-1g

wherein the parameters have the respective meanings given above.

In a preferred embodiment of the present invention the medium comprisescompounds selected from the group of compounds of formulae II-1a toII-1g wherein L²¹ and L²² or L²³ and L²⁴ are both F.

In another preferred embodiment the medium comprises compounds selectedfrom the group of compounds of formulae II-1a to II-1g, wherein L²¹,L²², L²³ and L²⁴ all are F.

Especially preferred compounds of formula II-1 are

wherein the R² has the meaning given above.

Preferably the compounds of formula II-2 are selected from the group ofcompounds of formulae II-2a to II-2c

wherein the parameters have the respective meanings given above andpreferably

L²¹ and L²² are both F.

Preferably the compounds of formula II-3 are selected from the group ofcompounds of formulae II-3a to II-3e

wherein the parameters have the respective meanings given above andpreferably

L²¹ and L²² are both F and L²³ and L²⁴ are both H or L²¹, L²², L²³ andL²⁴ are all F.

Especially preferred compounds of formula II-3 are

wherein the R² has the meaning given above.

In another preferred embodiment of the present invention compounds offormula III are selected from the group of formulae III-1 and III-2

wherein the parameters have the respective meanings given under formulaIII above.

Preferably the compounds of formula III-1 are selected from the group ofcompounds of formulae III-1a and III-1b

wherein the parameters have the respective meanings given above and theparameters L³³ and L³⁴, independently of each other and of the otherparameters, denote H or F.

Preferably the compounds of formula III-2 are selected from the group ofcompounds of formulae III-2a to III-2i

wherein the parameters have the respective meanings given above and L³⁵and L³⁶, independently of one another, denote H or F.

The compounds of formula III-1a, are preferably selected from the groupof compounds of formulae III-1a-1 to III-1a-6

wherein the R³ has the meaning given above.

In another preferred embodiment the compounds of formula II-2a areselected from the group of compounds of formulae III-2a-1 to III-2a-4

wherein the R³ has the meaning given above.

The compounds of formula III-2b are preferably selected from the groupof compounds of formulae III-2b-1 and III-2b-2, preferably III-2b-2

wherein the R³ has the meaning given above.

The compounds of formula II-2c, are preferably selected from the groupof compounds of formulae III-2c-1 to III-2c-5

wherein the R³ has the meaning given above.

The compounds of formulae III-2d and III-2e are preferably selected fromthe group of compounds of formulae III-2d-1 and III-2e-1

wherein the R³ has the meaning given above.

The compounds of formula III-2f are preferably selected from the groupof compounds of formulae III-2f-1 to III-2f-7

wherein the R³ has the meaning given above.

The compounds of formula III-2g, are preferably selected from the groupof compounds of formulae III-2g-1 to III-2g-5

wherein the R³ has the meaning given above.

The compounds of formula III-2h are preferably selected from the groupof compounds of formulae III-2h-1 to III-2h-3

wherein the R³ has the meaning given above.

The compounds of formula III-2i are preferably selected from the groupof compounds of formulae III-2i-1 to III-2i-6

wherein the R³ has the meaning given above.

Alternatively or additionally to compounds of formulae III-1 and/orIII-2 the media according to the present invention may comprise one ormore compounds of formula III-3,

wherein the parameters have the respective meanings given under formulaIII above,

and preferably of formula III-3a

wherein the R³ has the meaning given above.

Preferably the liquid crystalline media according to the presentinvention comprise one or more compounds of formula IV preferablyselected from the group of compounds of formulae IV-1 to IV-5

wherein R⁴¹ and R⁴² have the respective meanings given under formula IVabove and in formulae IV-1, IV-4 and IV-5 R⁴¹ preferably is alkyl oralkenyl, preferably alkenyl and R⁴² preferably is alkyl or alkenyl,preferably alkyl; in formula IV-2 R⁴¹ and R⁴² preferably are alkyl andin formula IV-3 R⁴¹ preferably is alkyl or alkenyl, preferably alkyl andR⁴² preferably is alkyl or alkoxy, preferably alkoxy.

In a preferred embodiment, the medium comprises one or more compounds offormula IV-1, more preferably selected from its respective subformulaeof formula CC-n-V and/or CC-nV-m, more preferably of formula CC-n-V andmost preferably of formula CC-3-V. The definitions of theseabbreviations (acronyms) are given in table B below.

In a preferred embodiment, the medium comprises one or more compounds offormula IV-4, more preferably selected from its respective subformulaeof formula CCP-V-n and/or CCP-nV-m and/or CCP-Vn-m, more preferably offormula CCP-V-n and/or CCP-V2-n and most preferably selected from thegroup of formulae CCP-V-1 and CCP-V2-1. The definitions of theseabbreviations (acronyms) are given in table B below.

Preferably the medium comprises compounds selected from the group ofcompounds of formulae IV-1, IV-3, IV-4 and IV-5, preferably one or morecompounds of formula IV-1 and one or more compounds selected from thegroup of formulae IV-3 or IV-4.

Optionally it can be preferred that the medium further comprises one ormore compounds of formula IV selected from the group of compounds offormulae IV-6 to IV-13

wherein

-   R⁴¹ and R⁴² independently of each other, denote alkyl, alkoxy,    fluorinated alkyl or fluorinated alkoxy with 1 to 7 C-atoms,    alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl with 2 to 7    C-atoms and-   L⁴ denotes H or F.

Alternatively or additionally to compounds of formulae II and/or III themedia according to the present invention my comprise one or morecompounds of formula V

wherein

-   R⁵ is alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy with 1    to 7 C-atoms, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated    alkenyl with 2 to 7 C-atoms, and preferably is alkyl or alkenyl,

are, independently of each other,

-   L⁵¹ and L⁵², independently of each other, denote H or F, preferably    L⁵¹ denotes F and-   X⁵ denotes halogen, halogenated alkyl or alkoxy with 1 to 3 C-atoms    or halogenated alkenyl or alkenyloxy with 2 or 3 C-atoms, preferably    F, Cl, —OCF₃ or —CF₃, most preferably F, Cl or —OCF₃,-   Z⁵ denotes —CH₂CH₂—, —CF₂CF₂—, —COO—, trans-—CH═CH—, trans-—CF═CF—    or —CH₂O, preferably —CH₂CH₂—, —COO— or trans-—CH═CH— and most    preferably —COO— or —CH₂CH₂—, and-   q is 0 or 1.

Preferably the media according to the present invention comprises one ormore compounds of formula V, preferably selected from the group ofcompounds of formulae V-1 and V-2

wherein the parameters have the respective meanings given above and theparameters L⁵³ and L⁵⁴ are, independently of each other and of the otherparameters, H or F and preferably Z⁵ is —CH₂—CH₂—.

Preferably the compounds of formula V-1 are selected from the group ofcompounds of formulae V-1a and V-1b

wherein the R⁵ has the meaning given above.

Preferably the compounds of formula V-2 are selected from the group ofcompounds of formulae V-2a to V-2d

wherein the R⁵ has the meaning given above.

Preferably the liquid crystalline media according to the presentinvention additionally comprise one or more compounds of formula VI

wherein

-   R⁶¹ and R⁶² independently of each other have the meaning given for    R² under formula II above, preferably R⁶¹ is alkyl and R⁶² is alkyl    or alkenyl,

in each occurrence independently of each other, denote to

-   Z⁶¹ and Z⁶² are, independently of each other, and in case Z⁶¹ is    present twice, also these independently of each other, —CH₂CH₂—,    —COO—, trans-—CH═CH—, trans-—CF═CF—, —CH₂O—, —CF₂O— or a single    bond, preferably at least one of them is a single bond, and-   r is 0, 1 or 2, preferably 0 or 1.

Preferably the compounds of formula VI are selected from the group ofcompounds of formulae VI-1 to VI-4

wherein R⁶¹ and R⁶² have the respective meanings given under formula VIabove and R⁶¹ preferably is alkyl and in formula VI-1 R⁶² preferably isalkenyl, preferably —(CH₂)₂—CH═CH—CH₃ and in formula VI-2 R⁶² preferablyis alkenyl, preferably —(CH₂)₂—CH═CH₂ and in formulae VI-3 and VI-4 R⁶²preferably is alkyl.

Preferably the medium comprises one or more compounds selected from thegroup of compounds of formulae VI-1 to VI-4 wherein R⁶¹ preferably isalkyl and in formula VI-1 R⁶² preferably is alkenyl, preferably—(CH₂)₂—CH═CH—CH₃ and in formula VI-2 R⁶² preferably is alkenyl,preferably —(CH₂)₂—CH═CH₂ and in formulae VI-3 and VI-4 R⁶² preferablyis alkyl.

The compounds of formula VI-1 are preferably selected from itssubformula PP-n-2Vm, more preferably of formula PP-1-2V1. Thedefinitions of these abbreviations (acronyms) are given in table Bbelow.

In a preferred embodiment, the medium comprises one or more compounds offormula VI-2, more preferably of its subformula PGP-n-m, more preferablyof its subformulae PGP-2-m and PGP-3-m, more preferably selected from offormulae PGP-2-2V, PGP-3-2, PGP-3-3, PGP-3-4, PGP-3-5.

The definitions of these abbreviations (acronyms) are given in table Bbelow.

Medium

Preferably the liquid crystalline media according to the instantinvention comprise one or more compounds of formula I, II, III and IV.

Also other mesogenic compounds, which are not explicitly mentionedabove, can optionally and beneficially be used in the media according tothe instant invention. Such compounds are known to the expert in thefield.

The Δn, at 589 nm (Na^(D)) and 20° C., of the liquid crystal mediaaccording to the instant invention preferably is in the range of 0.070or more to 0.145 or less, more preferably in the range of 0.080 or moreto 0.140 or less and most preferably in the range of 0.090 or more to0.135 or less.

The Δε, at 1 kHz and 20° C., of the liquid crystal medium according tothe invention preferably is 4 or more, more preferably 6 or more andmost preferably 8 or more. In particular Δε is 14 or less.

Preferably the nematic phase of the inventive media extends at leastfrom 0° C. or less to 70° C. more, more preferably at least from −20° C.or less to 70° C. more, most preferably at least from −30° C. or less to75° C. more and in particular at least from −40° C. or less to 75° C.more.

In a first preferred embodiment of the present invention the An of theliquid crystal media is in the range of 0.120 or more to 0.150 or less,more preferably in the range of 0.125 or more to 0.145 or less and mostpreferably in the range of 0.130 or more to 0.140 or less, while Acpreferably is in the range from 3 or more to 12 or less, preferably 10or less.

In a second preferred embodiment of the present invention the An of theliquid crystal media is n the range of 0.120 or more to 0.150 or less,more preferably in the range of 0.125 or more to 0.145 or less and mostpreferably in the range of 0.130 or more to 0.140 or less, while Acpreferably is in the range from 2 or more to 8 or less, preferably 6 orless.

In a third preferred embodiment of the present invention the An of theliquid crystal media is n the range of 0.085 or more to 0.130 or less,more preferably in the range of 0.090 or more to 0.125 or less and mostpreferably in the range of 0.095 or more to 0.120 or less, while Acpreferably is 6 or more, more preferably 8 or more, even more preferably11 or more and most preferably in the range from 11 or more to 14 orless.

In a fourth preferred embodiment of the present invention the An of theliquid crystal media is n the range of 0.090 or more to 0.135 or less,more preferably in the range of 0.095 or more to 0.130 or less and mostpreferably in the range of 0.110 or more to 0.125 or less, while Acpreferably is 6 or more, more preferably 8 or more, even more preferably11 or more and most preferably in the range from 11 or more to 14 orless.

The concentration of compounds of formula I in the medium preferably isin the range from 1% to 20%, more preferably from 2% to 17% and mostpreferably from 4% to 15%.

The total concentration of compounds of formulae II and III in themedium preferably is in the range from 5% to 65%, more preferably from10% to 60% and most preferably from 13% to 50%.

The total concentration of compounds of the formulae I, II and III intotal preferably is in the range from from 10% to 80%, more preferablyfrom 15% to 70% and most preferably from 18% to 65%

The total concentration of compounds of formula IV preferably is in therange from 30% to 70%, more preferably from 35% to 60% and mostpreferably from 40% to 55%.

The total concentration of compounds of formula V is in the range from0% to 35%, more preferably from 1% to 30% and most preferably from 5% to30%.

The concentration of compounds of formula VI is in the range from 0 to40%, preferably 2 to 35% and most preferably 5 to 30%.

Optionally, the inventive media can comprise further liquid crystalcompounds in order to adjust the physical properties. Such compounds areknown to the expert. Their concentration in the media according to theinstant invention is preferably 0% to 30%, more preferably 0.1% to 20%and most preferably 1% to 15%.

In a preferred embodiment the medium comprises one or more compounds offormula IV, more preferably of formula IV-1, more preferably selectedfrom its respective subformulae of formula CC-n-V and/or CC-n-Vm, morepreferably of formula CC-n-V1 and/or CC-n-V and most preferably selectedfrom the group of formulae CC-3-V, CC-4-V, CC-S-V and CC-3-V1.

In a preferred embodiment the medium comprises one or more compounds offormula II-1, preferably of formulae II-1a and III-g, more preferably offormula II-1-g-1, preferably selected from its respective subformulae offormula PGUQU-n-F, most preferably selected from the group of formulaePGUQU-3-F, PGUQU-4-F and PGUQU-5-F.

The definitions of these abbreviations (acronyms) are given in table Bbelow. In this preferred embodiment, preferably the concentration ofcompounds of formula IV is greater than 40%, more preferably greaterthan 42%, and most preferably greater than 45%.

Preferably the liquid crystal media contain 50% to 100%, more preferably70% to 100% and most preferably 90% to 100% compounds of formulae Ito VIand preferably Ito IV and VI.

In the present application the term dielectrically positive meanscompounds or components with Δε>3.0, dielectrically neutral with−1,5≤Δε≤3.0 and dielectrically negative with Δε≤−1,5. Δε is determinedat a frequency of 1 kHz and at 20° C. The dielectric anisotropy of therespective compound is determined from the results of a solution of 10%of the respective individual compound in a nematic host mixture. In casethe solubility of the respective compound in the host mixture is lessthan 10% the concentration is reduced to 5%. The capacities of the testmixtures are determined both in a cell with homeotropic and withhomogeneous alignment. The cell gap of both types of cells isapproximately 20 μm. The voltage applied is a rectangular wave with afrequency of 1 kHz and a root mean square value typically of 0.5 V to1.0 V, however, it is always selected to be below the capacitivethreshold of the respective test mixture.

Δε is defined as (ε∥−ε_(⊥)), whereas ε_(av.) is (ε∥+2ε_(⊥))/3.

For dielectrically positive compounds the mixture ZLI-4792 and fordielectrically neutral, as well as for dielectrically negativecompounds, the mixture ZLI-3086, both of Merck KGaA, Germany are used ashost mixture, respectively. The dielectric permittivities of thecompounds are determined from the change of the respective values of thehost mixture upon addition of the compounds of interest. The values areextrapolated to a concentration of the compounds of interest of 100%.

Components having a nematic phase at the measurement temperature of 20°C. are measured as such, all others are treated like compounds.

The term threshold voltage refers in the instant application to theoptical threshold and is given for 10% relative contrast (V₁₀, alsoabbreviated to V_((10,0,20)) indicating perpendicular observation and20° C.) and the term saturation voltage refers to the optical saturationand is given for 90% relative contrast (V₉₀, also abbreviated toV_((90,0,20)) indicating perpendicular observation and 20° C.) both, ifnot explicitly stated otherwise. The capacitive threshold voltage (V₀),also called Freedericksz-threshold (V_(Fr)) is only used if explicitlymentioned.

The following abbreciations are used:

-   V_(op)=operating voltage;-   t_(on)=time after switching on until 90% of the maximum contrast is    achieved, measured from 10% of the maximum contrast;-   t_(off)=time after switching off until 10% of the maximum contrast    is achieved, measured from 90% of the maximum contrast;-   t_(sum)=t_(on+)t_(off).

The ranges of parameters given in this application are all including thelimiting values, unless explicitly stated otherwise.

Throughout this application, unless explicitly stated otherwise, allconcentrations are given in mass percent and relate to the respectivecomplete mixture, all temperatures are given in degrees centigrade(Celsius) and all differences of temperatures in degrees centigrade. Allphysical properties have been and are determined according to “MerckLiquid Crystals, Physical Properties of Liquid Crystals”, StatusNovember 1997, Merck KGaA, Germany and are given for a temperature of20° C., unless explicitly stated otherwise. The optical anisotropy (Δn)is determined at a wavelength of 589.3 nm. The dielectric anisotropy(Δε) is determined at a frequency of 1 kHz. The threshold voltages, aswell as all other electro-optical properties have been determined withtest cells prepared at Merck KGaA, Germany. The test cells for thedetermination of Δε had a cell gap of approximately 20 μm. The electrodewas a circular ITO electrode with an area of 1.13 cm² and a guard ring.The orientation layers were lecithin for homeotropic orientation (ε∥)and polyimide AL-1054 from Japan Synthetic Rubber for homogeneousorientation (ε_(⊥)). The capacities were determined with a frequencyresponse analyser Solatron 1260 using a sine wave with a voltage of 0.3V_(rms). The light used in the electro-optical measurements was whitelight. The set up used was commercially available equipment of Otsuka,Japan. The characteristic voltages have been determined underperpendicular observation. The threshold (V₁₀)-mid grey (V₅₀)—andsaturation (V₉₀) voltages have been determined for 10%, 50% and 90%relative contrast, respectively.

The liquid crystal media according to the present invention can containfurther additives and chiral dopants in usual concentrations. The totalconcentration of these further constituents is in the range of 0% to10%, preferably 0.1% to 6%, based on the total mixture. Theconcentrations of the individual compounds used each are preferably inthe range of 0.1% to 3%. The concentration of these and of similaradditives is not taken into consideration for the values and ranges ofthe concentrations of the liquid crystal components and compounds of theliquid crystal media in this application.

The inventive liquid crystal media according to the present inventionconsist of several compounds, preferably of 3 to 30, more preferably of4 to 20 and most preferably of 4 to 16 compounds. These compounds aremixed in conventional way. As a rule, the required amount of thecompound used in the smaller amount is dissolved in the compound used inthe greater amount. In case the temperature is above the clearing pointof the compound used in the higher concentration, it is particularlyeasy to observe completion of the process of dissolution. It is,however, also possible to prepare the media by other conventional ways,e.g. using so called pre-mixtures, which can be e.g. homologous oreutectic mixtures of compounds or using so called multi-bottle-systems,the constituents of which are ready to use mixtures themselves.

By addition of suitable additives, the liquid crystal media according tothe instant invention can be modified in such a way, that they areusable in all known types of liquid crystal displays, either using theliquid crystal media as such, like TN-, TN-AMD, ECB-AMD, VAN-AMD, IPSand OCB LCDs and in particular in composite systems, like PDLC, NCAP, PNLCDs and especially in ASM-PA LCDs.

The melting point T(C,N), the transition from the smectic (S) to thenematic (N) phase T(S,N) and the clearing point T(N,I) of the liquidcrystals are given in degrees centigrade.

In the present application and especially in the following examples, thestructures of the liquid crystal compounds are represented byabbreviations also called acronyms. The transformation of theabbreviations into the corresponding structures is straight forwardaccording to the following two tables A and B. All groups C_(n)H_(2n+1)and C_(m)H_(2m+1) are straight chain alkyl groups with n respectively mC-atoms. The interpretation of table B is self-evident. Table A doesonly list the abbreviations for the cores of the structures. Theindividual compounds are denoted by the abbreviation of the corefollowed by a hyphen and a code specifying the substituents R¹, R², L¹and L² as followsollows:

Code for R¹, R², L¹, L² R¹ R² L¹ L² nm C_(n)H_(2n+1) C_(m)H_(2m+1) H HnOm C_(n)H_(2n+1) OC_(m)H_(2m+1) H H nO · m OC_(n)H_(2n+1) C_(m)H_(2m+1)H H n C_(n)H_(2n+1) CN H H nN · F C_(n)H_(2n+1) CN H F nN · F · FC_(n)H_(2n+1) CN F F nF C_(n)H_(2n+1) F H H nF · F C_(n)H_(2n+1) F H FnF · F · F C_(n)H_(2n+1) F F F nOF OC_(n)H_(2n+1) F H H nClC_(n)H_(2n+1) Cl H H nCl · F C_(n)H_(2n+1) Cl H F nCl · F · FC_(n)H_(2n+1) Cl F F nCF₃ C_(n)H_(2n+1) CF₃ H H nCF₃ · F C_(n)H_(2n+1)CF₃ H F nCF₃ · F · F C_(n)H_(2n+1) CF₃ F F nOCF₃ C_(n)H_(2n+1) OCF₃ H HnOCF₃ · F C_(n)H_(2n+1) OCF₃ H F nOCF₃ · F · F C_(n)H_(2n+1) OCF₃ F FnOCF₂ C_(n)H_(2n+1) OCHF₂ H H nOCF₂ · F C_(n)H_(2n+1) OCHF₂ H F nOCF₂ ·F · F C_(n)H_(2n+1) OCHF₂ F F nS C_(n)H_(2n+1) NCS H H nS · FC_(n)H_(2n+1) NCS H F nS · F · F C_(n)H_(2n+1) NCS F F rVsNC_(r)H_(2r+1)—CH═CH—C_(s)H_(2s)— CN H H rEsNC_(r)H_(2r+1)—O—C_(s)H_(2s)— CN H H nAm C_(n)H_(2n+1) COOC_(m)H_(2m+1) HH

TABLE A

TABLE B

TABLE C

Table C shows possible stabilisers which can be added to the LC mediaaccording to the invention.

-   (n here denotes an integer from 1 to 12, preferably 1, 2, 3, 4, 5,    6, 7 or 8, terminal methyl groups are not shown).

The LC media preferably comprise 0 to 10% by weight, in particular 1 ppmto 5% by weight, particularly preferably 1 ppm to 1% by weight, ofstabilisers. The LC media preferably comprise one or more stabilisersselected from the group consisting of compounds from Table C

The liquid crystal media according to the instant invention containpreferably

-   -   seven or more, preferably eight or more compounds, preferably of        different formulae, selected from the group of compounds of        tables A and B and/or    -   one or more, more preferably two or more, preferably three or        more compounds, preferably of different formulae, selected from        the group of compounds of table A and/or    -   three or more, more preferably four or more compounds, more        preferably five or more compounds, preferably of different        formulae, selected from the group of compounds of table B.

EXAMPLES

The examples given in the following are illustrating the presentinvention without limiting it in any way.

However, the physical properties compositions illustrate to the expert,which properties can be achieved and in which ranges they can bemodified. Especially the combination of the various properties, whichcan be preferably achieved, is thus well defined for the expert.

Example 1

A liquid crystal mixture is realized with the composition and propertiesgiven in the following table.

Composition Compound No. Abbreviation Conc./% 1 CC-3-V 40.50 2 CC-3-V18.00 3 CCP-V2-1 3.50 4 CPGU-3-OT 5.00 5 PGP-2-2V 20.00 6 PGUQU-3-F 8.007 PP-1-2V1 10.00 8 PUQU-3-T 5.00 Σ 100.00 Physical Properties T(N, I) =75.5° C. Δn (20° C., 589.3 nm) = 0.1318 ε _(| |) (20° C., 1 kHz) = 7.6Δε (20° C., 1 kHz) = 4.7 γ₁ (20° C.) = 54 mPa · s V_((10, 0, 20)) = 2.04V V_((90, 0, 20)) = 3.03 V γ₁/[Δε (V₁₀)²] = 2.76 mPa · s V⁻² t_(on)(V_(op) = 5.0 V) = 1.50 ms t_(off) (V_(op) = 5.0 V) = 3.89 ms t_(sum)(V_(op) = 5.0 V) = 5.39 ms

Example 2

A liquid crystal mixture is realized with the composition and propertiesgiven in the following table.

Composition Compound No. Abbreviation Conc./% 1 CC-3-V 40.00 2 CC-3-V18.00 3 CCP-V2-1 4.00 4 CPGU-3-OT 5.00 5 PGP-2-2V 20.00 6 PGUQU-3-F 8.007 PP-1-2V1 10.00 8 GUQU-3-T 5.00 Σ 100.00 Physical Properties T(N, I) =75.0° C. Δn (20° C., 589.3 nm) = 0.1309 ε _(| |) (20° C., 1 kHz) = 7.7Δε (20° C., 1 kHz) = 4.7 γ₁ (20° C.) = 55 mPa · s V_((10, 0, 20)) = 2.02V V_((90, 0, 20)) = 3.00 V γ₁/[Δε (V₁₀)²] = 2.86 mPa · s V⁻²

Example 3

A liquid crystal mixture is realized with the composition and propertiesgiven in the following table.

Composition Compound No. Abbreviation Conc./% 1 CC-3-V 47.50 2 PP-1-2V15.00 3 PGP-2-2V 19.00 4 PGUQU-3-F 13.00 5 CPGU-3-OT 4.00 6 APUQU-3-F5.50 7 PUQU-3-T 6.00 Σ 100.00 Physical Properties T(N, I) = 74.5° C. Δn(20° C., 589.3 nm) = 0.1322 ε _(| |) (20° C., 1 kHz) = 11.3   Δε (20°C., 1 kHz) = 8.1   γ₁ (20° C.) = 60 mPa · s V_((10, 0, 20)) = 1.55 VV_((90, 0, 20)) = 2.31 V γ₁/[Δε (V₁₀)²] = 3.10 mPa · s V⁻² t_(on)(V_(op) = 4.5 V) = 1.22 ms t_(off) (V_(op) = 4.5 V) = 4.67 ms t_(sum)(V_(op) = 4.5 V) = 5.88 ms

Example 4 A liquid crystal mixture is realized with the composition andproperties given in the following table.

Composition Compound No. Abbreviation Conc./% 1 CC-3-V 47.00 2 PP-1-2V16.00 3 PGP-2-2V 19.00 4 PGUQU-3-F 12.00 5 CPGU-3-OT 5.00 6 APUQU-3-F5.50 7 GUQU-3-T 5.50 Σ 100.00 Physical Properties T(N, I) = 74.0° C. Δn(20° C., 589.3 nm) = 0.1327 ε _(| |) (20° C., 1 kHz) = 11.2 Δε (20° C.,1 kHz) = 7.9 γ₁ (20° C.) = 60 mPa · s V_((10, 0, 20)) = 1.56 VV_((90, 0, 20)) = 2.34 V γ₁/[Δε (V₁₀)²] = 3.13 mPa · s V⁻²

Example 5

A liquid crystal mixture is realized with the composition and propertiesgiven in the following table.

Composition Compound No. Abbreviation Conc./% 1 CC-3-V 42.00 2 PUQU-3-T14.50 3 CCP-V-1 9.00 4 APUQU-2-F 6.00 5 APUQU-3-F 8.50 6 PGUQU-3-F 9.507 CPGU-3-OT 5.00 8 PGP-2-2V 5.50 Σ 100.00 Physical Properties T(N, I) =74.5° C. Δn (20° C., 589.3 nm) = 0.1149 ε _(| |) (20° C., 1 kHz) = 17.6Δε (20° C., 1 kHz) = 13.7 γ₁ (20° C.) = 77 mPa · s V_((10, 0, 20)) =1.18 V V_((90, 0, 20)) = 1.81 V γ₁/[Δε (V₁₀)²] = 4.06 mPa · s V⁻²

Example 6

A liquid crystal mixture is realized with the composition and propertiesgiven in the following table.

Composition Compound No. Abbreviation Conc./% Physical Properties 1CC-3-V 42.50 T(N, I) = 74.0° C. 2 GUQU-3-T 13.00 Δn (20° C., 589.30.1150 3 CCP-V-1 8.00 nm) = 4 APUQU-2-F 6.00 ε∥ (20° C., 1 kHz) = 17.6 5APUQU-3-F 9.00 Δε (20° C., 1 kHz) = 13.6 6 PGUQU-3-F 9.00 γ₁ (20° C.) =75 mPa · s 7 CPGU-3-OT 5.50 V_((10, 0, 20)) = 1.17 V 8 PGP-2-2V 7.00V_((90, 0, 20)) = 1.80 V Σ 100.00 γ₁/[Δε (V₁₀)²] = 4.03 mPa · s V⁻²

Example 7

A liquid crystal mixture is realized with the composition and propertiesgiven in the following table.

Composition Compound No. Abbreviation Conc./% Physical Properties 1CC-3-V 42.50 T(N, I) = 74.5° C. 2 CCP-V-1 12.00 Δn (20° C., 589.3 0.11523 PP-1-2V1 2.50 nm) = 4 PUQU-3-T 8.00 ε∥ (20° C., 1 kHz) = 17.2 5PGUQU-3-F 8.50 Δε (20° C., 1 kHz) = 13.6 6 PGUQU-4-F 8.50 γ₁ (20° C.) =75 mPa · s 7 PGUQU-5-F 8.50 V_((10, 0, 20)) = 1.19 V 8 APUQU-3-F 9.50V_((90, 0, 20)) = 1.84 V Σ 100.00 γ₁/[Δε (V₁₀)²] = 4.10 mPa · s V⁻²t_(on) (V_(op) = 3.3 V) =  2.21 ms t_(off) (V_(op) = 3.3 V) =  7.89 mst_(sum) (V_(op) = 3.3 V) = 10.10 ms

Example 8

A liquid crystal mixture is realized with the composition and propertiesgiven in the following table.

Composition Compound No. Abbreviation Conc./% Physical Properties 1CC-3-V 45.50 T(N, I) = 75.0° C. 2 CCP-V-1 9.50 Δn (20° C., 589.3 0.11493 GUQU-3-T 7.50 nm) = 4 PGUQU-3-F 7.50 ε∥ (20° C., 1 kHz) = 16.5 5PGUQU-4-F 8.00 Δε (20° C., 1 kHz) = 12.7 6 PGUQU-5-F 8.50 γ₁ (20° C.) =73 mPa · s 7 APUQU-3-F 9.00 V_((10, 0, 20)) = 1.22 V 8 PGP-2-2V 4.50V_((90, 0, 20)) = 1.89 V Σ 100.00 γ₁/[Δε (V₁₀)²] = 3.85 mPa · s V⁻²

Example 9

A liquid crystal mixture is realized with the composition and propertiesgiven in the following table.

Composition Compound No. Abbreviation Conc./% Physical Properties 1CC-3-V 44.50 T(N, I) = 74.5° C. 2 APUQU-2-F 6.50 Δn (20° C., 589.30.1143 3 APUQU-3-F 8.00 nm) = 4 CPGU-3-OT 4.50 ε∥ (20° C., 1 kHz) = 16.25 PGUQU-3-F 8.50 Δε (20° C., 1 kHz) = 12.4 6 PUQU-3-T 6.00 γ₁ (20° C.) =69 mPa · s 7 PGP-2-2V 2.00 V_((10, 0, 20)) = 1.19 V 8 CPU-3-OXF 20.00V_((90, 0, 20)) = 1.82 V Σ 100.00 γ₁/[Δε (V₁₀)²] = 3.97 mPa · s V⁻²

Example 10

A liquid crystal mixture is realized with the composition and propertiesgiven in the following table.

Composition Compound No. Abbreviation Conc./% Physical Properties 1CC-3-V 44.50 T(N, I) = 74.5° C. 2 APUQU-2-F 6.50 Δn (20° C., 589.30.1141 3 APUQU-3-F 8.00 nm) = 4 CPGU-3-OT 4.50 ε∥ (20° C., 1 kHz) = 16.45 PGUQU-3-F 8.50 Δε (20° C., 1 kHz) = 12.5 6 GUQU-3-T 5.50 γ₁ (20° C.) =69 mPa · s 7 PGP-2-2V 2.00 V_((10, 0, 20)) = 1.19 V 8 CPU-3-OXF 20.50V_((90, 0, 20)) = 1.81 V Σ 100.00 γ₁/[Δε (V₁₀)²] = 3.91 mPa · s V⁻²

Example 11

A liquid crystal mixture is realized with the composition and propertiesgiven in the following table.

Composition Compound No. Abbreviation Conc./% Physical Properties 1CC-3-V 43.50 T(N, I) = 75.0° C. 2 CCP-V-1 4.00 Δn (20° C., 589.3 0.11513 PUQU-3-T 4.50 nm) = 4 PGUQU-3-F 6.00 ε∥ (20° C., 1 kHz) = 16.0 5PGUQU-4-F 6.50 Δε (20° C., 1 kHz) = 12.2 6 PGUQU-5-F 7.00 γ₁ (20° C.) =70 mPa · s 7 APUQU-3-F 8.00 V_((10, 0, 20)) = 1.20 V 8 CPU-3-OXF 20.50V_((90, 0, 20)) = 1.85 V Σ 100.00 γ₁/[Δε (V₁₀)²] = 3.98 mPa · s V⁻²

Example 12

A liquid crystal mixture is realized with the composition and propertiesgiven in the following table.

Composition Compound No. Abbreviation Conc./% Physical Properties 1CC-3-V 43.00 T(N, I) = 75.0° C. 2 CCP-V-1 4.50 Δn (20° C., 589.3 0.11503 GUQU-3-T 4.50 nm) = 4 PGUQU-3-F 6.00 ε∥ (20° C., 1 kHz) = 16.2 5PGUQU-4-F 6.50 Δε (20° C., 1 kHz) = 12.3 6 PGUQU-5-F 7.00 γ₁ (20° C.) =70 mPa · s 7 APUQU-3-F 8.00 V_((10, 0, 20)) = 1.20 V 8 CPU-3-OXF 20.50V_((90, 0, 20)) = 1.84 V Σ 100.00 γ₁/[Δε (V₁₀)²] = 3.97 mPa · s V⁻²

Example 13

A liquid crystal mixture is realized with the composition and propertiesgiven in the following table.

Composition Compound No. Abbreviation Conc./% Physical Properties 1CC-3-V 40.00 T(N, I) = 74.5 ° C. 2 PGP-2-2V 11.50 Δn (20° C., 589.30.1255 3 PUQU-3-T 12.00 nm) = 4 CCP-V-1 3.50 ε∥ (20° C., 1 kHz) = 17.4 5APUQU-2-F 6.00 Δε (20° C., 1 kHz) = 13.5 6 APUQU-3-F 8.00 γ₁ (20° C.) =78 mPa · s 7 PGUQU-3-F 9.50 V_((10, 0, 20)) = 1.17 V 8 CPGU-3-OT 4.00V_((90, 0, 20)) = 1.79 V 9 CPU-3-F 5.50 γ₁/[Δε (V₁₀)²] = 4.18 mPa · Σ100.00 s V⁻²

Example 14

A liquid crystal mixture is realized with the composition and propertiesgiven in the following table.

Composition Compound No. Abbreviation Conc./% Physical Properties 1CC-3-V 41.00 T(N, I) = 74.5° C. 2 PGP-2-2V 13.50 Δn (20° C., 589.30.1253 3 GUQU-3-T 11.00 nm) = 4 CCP-V-1 3.50 ε∥ (20° C., 1 kHz) = 17.4 5APUQU-2-F 6.50 Δε (20° C., 1 kHz) = 13.1 6 APUQU-3-F 8.00 γ₁ (20° C.) =75 mPa · s 7 PGUQU-3-F 9.00 V_((10, 0, 20)) = 1.19 V 8 CPGU-3-OT 4.00V_((90, 0, 20)) = 1.82 V 9 CPU-3-F 3.50 γ₁/[Δε (V₁₀)²] = 4.08 mPa · Σ100.00 s V⁻²

Example15

A liquid crystal mixture is realized with the composition and propertiesgiven in the following table.

Composition Compound No. Abbreviation Conc./% Physical Properties 1CC-3-V 43.50 T(N, I) = 74.5° C. 2 CCP-V-1 5.00 Δn (20° C., 589.3 0.12553 PGP-2-2V 9.50 nm) = 4 PUQU-3-T 9.50 ε∥ (20° C., 1 kHz) = 17.4 5PGUQU-3-F 7.00 Δε (20° C., 1 kHz) = 13.7 6 PGUQU-4-F 8.50 γ₁ (20° C.) =77 mPa · s 7 PGUQU-5-F 9.00 V_((10, 0, 20)) = 1.18 V 8 APUQU-3-F 8.00V_((90, 0, 20)) = 1.81 V Σ 100.00 γ₁/[Δε (V₁₀)²] = 4.05 mPa · s V⁻²t_(on) (V_(op) = 3.3 V) = 1.83 ms t_(off) (V_(op) = 3.3 V) = 6.64 mst_(sum) (V_(op) = 3.3 V) = 8.47 ms

Example 16

A liquid crystal mixture is realized with the composition and propertiesgiven in the following table.

Composition Compound No. Abbreviation Conc./% Physical Properties 1CC-3-V 44.00 T(N, I) = 74.5° C. 2 CCP-V-1 6.00 Δn (20° C., 589.3 0.12513 PGP-2-2V 11.00 nm) = 4 GUQU-3-T 8.50 ε∥ (20° C., 1 kHz) = 16.3 5PGUQU-3-F 7.00 Δε (20° C., 1 kHz) = 12.6 6 PGUQU-4-F 8.00 γ₁ (20° C.) =73 mPa · s 7 PGUQU-5-F 9.00 V_((10, 0, 20)) = 1.23 V 8 APUQU-3-F 6.50V_((90, 0, 20)) = 1.88 V Σ 100.00 γ₁/[Δε (V₁₀)²] = 3.87 mPa · s V⁻²

Example 17

A liquid crystal mixture is realized with the composition and propertiesgiven in the following table.

Composition Compound No. Abbreviation Conc./% Physical Properties 1CC-3-V 39.50 T(N, I) = 75.5° C. 2 APUQU-2-F 5.00 Δn (20° C., 589.30.1260 3 APUQU-3-F 6.00 nm) = 4 CPGU-3-OT 3.50 ε∥ (20° C., 1 kHz) = 17.05 PGUQU-3-F 9.50 Δε (20° C., 1 kHz) = 13.0 6 PUQU-3-T 9.00 γ₁ (20° C.) =72 mPa · s 7 PGP-2-2V 7.50 V_((10, 0, 20)) = 1.19 V 8 CPU-3-OXF 20.00V_((90, 0, 20)) = 1.79 V Σ 100.00 γ₁/[Δε (V₁₀)²] = 3.95 mPa · s V⁻²

Example 18

A liquid crystal mixture is realized with the composition and propertiesgiven in the following table.

Composition Compound No. Abbreviation Conc./% Physical Properties 1CC-3-V 39.50 T(N, I) = 76.0° C. 2 APUQU-2-F 5.00 Δn (20° C., 589.30.1260 3 APUQU-3-F 6.00 nm) = 4 CPGU-3-OT 4.50 ε∥ (20° C., 1 kHz) = 16.85 PGUQU-3-F 8.50 Δε (20° C., 1 kHz) = 12.7 6 GUQU-3-T 9.00 γ₁ (20° C.) =70 mPa · s 7 PGP-2-2V 8.50 V_((10, 0, 20)) = 1.19 V 8 CPU-3-OXF 19.00V_((90, 0, 20)) = 1.78 V Σ 100.00 γ₁/[Δε (V₁₀)²] = 3.91 mPa · s V⁻²

Example 19

A liquid crystal mixture is realized with the composition and propertiesgiven in the following table.

Composition Compound No. Abbreviation Conc./% Physical Properties 1CC-3-V 41.50 T(N, I) = 75.0° C. 2 APUQU-3-F 4.00 Δn (20° C., 589.30.1247 3 PGUQU-3-F 7.00 nm) = 4 PGUQU-4-F 7.00 ε∥ (20° C., 1 kHz) = 16.55 PGUQU-5-F 8.00 Δε (20° C., 1 kHz) = 12.6 6 PUQU-3-T 4.50 γ₁ (20° C.) =71 mPa · s 7 PGP-2-2V 3.50 V_((10, 0, 20)) = 1.19 V 8 CPU-3-OXF 24.50V_((90, 0, 20)) = 1.81 V Σ 100.00 γ₁/[Δε (V₁₀)²] = 4.00 mPa · s V⁻²

Example 20

A liquid crystal mixture is realized with the composition and propertiesgiven in the following table.

Composition Compound No. Abbreviation Conc./% Physical Properties 1CC-3-V 41.00 T(N, I) = 75.0° C. 2 APUQU-3-F 4.00 Δn (20° C., 589.30.1251 3 PGUQU-3-F 7.00 nm) = 4 PGUQU-4-F 7.00 ε∥ (20° C., 1 kHz) = 16.75 PGUQU-5-F 8.00 Δε (20° C., 1 kHz) = 12.9 6 GUQU-3-T 4.50 γ₁ (20° C.) =72 mPa · s 7 PGP-2-2V 4.00 V_((10, 0, 20)) = 1.19 V 8 CPU-3-OXF 24.50V_((90, 0, 20)) = 1.80 V Σ 100.00 γ₁/[Δε (V₁₀)²] = 3.99 mPa · s V⁻²

1. Liquid crystal medium, characterised in that it comprises a compoundof formula I

wherein R¹ denotes alkyl, alkoxy, fluorinated alkyl or fluorinatedalkoxy with 1 to 7 C-atoms, alkenyl, alkenyloxy, alkoxyalkyl orfluorinated alkenyl with 2 to 7 C-atoms, L¹ denotes H or F.
 2. Liquidcrystal medium according to claim 1, characterised in that L¹ in formulaI denotes H.
 3. Liquid crystal medium according to claim 1,characterised in that it additionally comprises one or more compoundsselected from the group of compounds of formulae II and III

wherein R² and R³, independently of each other, are alkyl, alkoxy,fluorinated alkyl or fluorinated alkoxy with 1 to 7 C-atoms, alkenyl,alkenyloxy, alkoxyalkyl or fluorinated alkenyl with 2 to 7 C-atoms,

are, independently of each other,

L²¹, L²², L³¹ and L³², are, independently of each other, H or F, X² andX³ are, independently of each other, halogen, halogenated alkyl oralkoxy with 1 to 3 C-atoms or halogenated alkenyl or alkenyloxy with 2or 3 C-atoms, Z³ is —CH₂CH₂—, —CF₂CF₂—, —COO—, trans-—CH═CH—,trans-—CF═CF—, —CH₂O— or a single bond, and 1, m, n and o are,independently of each other, 0 or 1 and from which compounds of formulaI are excluded.
 4. Liquid crystal medium according to claim 3characterised in that it comprises one or more compounds of formula II.5. Liquid crystal medium according to claim 3, characterised in that itcomprises one or more compounds of formula III.
 6. Liquid crystal mediumaccording to claim 3, characterised in that one or more compounds offormula II are selected from compounds of formula II-1g-1

wherein R² is defined as for formula II.
 7. Liquid crystal mediumaccording to claim 1, characterised in that it additionally comprisesone or more compounds of formula IV

wherein R⁴¹ and R⁴², independently of each other, are alkyl, alkoxy,fluorinated alkyl or fluorinated alkoxy with 1 to 7 C-atoms, alkenyl,alkenyloxy, alkoxyalkyl or fluorinated alkenyl with 2 to 7 C-atoms.

independently of each other, and in case

is present twice, also these, independently of each other, are

Z⁴¹ and Z⁴² independently of each other, and in case Z⁴¹ is presenttwice, also these independently of each other, denote —CH₂CH₂—, —COO—,trans-—CH═CH—, trans-—CF═CF—, —CH₂O—, —CF₂O—, —C≡C— or a single bond,and p is 0, 1 or
 2. 8. Liquid crystal medium according to claim 7,characterised in that one or more compounds of formula IV are selectedfrom the group of compounds of formulae IV-1 to IV-5.

wherein R⁴¹ and R⁴² are as difined for formula IV.
 9. Liquid crystalmedium according to claim 1, characterised in that it comprises one ormore compounds of formula VI

wherein R⁶¹ and R⁶², independently of each other, are alkyl, alkoxy,fluorinated alkyl or fluorinated alkoxy with 1 to 7 C-atoms, alkenyl,alkenyloxy, alkoxy alkyl or fluorinated alkenyl with 2 to 7 C-atoms.

in each occurrence independently of each other, denote

Z⁶¹ and Z⁶² independently of each other, denote —CH₂CH₂—, —COO—,trans-—CH═CH—, trans-—CF═CF—, —CH₂O—, —CF₂O, —C≡C— or a single bond, andr is 0, 1 or
 2. 10. Liquid crystal medium according to claim 9,characterised in that one or more compounds of formula VI are selectedfrom the group of compounds of formulae VI-1 to VI-4

wherein R⁶¹ and R⁶² are defined for formula VI.
 11. Liquid crystalmedium according to claim 1, characterised in that the totalconcentration of the compounds of formula I in the medium is in therange from 1% to 20%.
 12. Process for the preparation of aliquid-crystalline medium according to claim 1, characterised in that atleast one compound of the formula I is mixed with at least one furthermesogenic compound, and one or more additives and/or one or morestabilisers are optionally added.
 13. Liquid crystal display,characterised in that it comprises a liquid crystal medium according toclaim
 1. 14. Liquid crystal display according to claim 13, characterisedin that it is addressed by an active matrix.
 15. (canceled)